Profiled rigid or semi-rigid thermoplastics material tube is used for a number uses such as for electrical conduit and for drainage tube. It is frequently desirable or necessary to use profiled tube for strength reasons. The tube may be profiled as single walled corrugated tube, double walled corrugated tube, ribbed tube, or sometimes smooth walled tube may be used. Any ribs or corrugations on the tube may be helical or annular. Often, the molding and profiling is done by extruding a parison of extrudate into a travelling mold tunnel into which an elongate extrusion nozzle from an extrusion die extends to direct a parison of thermoplastic material against an inner wall of the mold tunnel.
The extrusion nozzle is usually different for different purposes. For example, an extrusion nozzle which is suitable for use with a travelling mold tunnel structured to mold ribbed tube, may be considerably different than one intended for other purposes. Moreover, it may be preferable for at least some purposes, for example the molding of ribbed tube, that the exit angle of the extrusion nozzle be 450 or more. For the molding of double walled corrugated tube, it may be desirable to provide a splitter to divide the flow of extrudate from the extrusion die into two coaxial streams. Many other variations are sometimes required.
To make the above-mentioned variations in the structure of the extrusion nozzle and, indeed, various other modifications, it has been necessary to dismantle the apparatus and change the extrusion nozzle at the point of its connection to the extrusion die. Shutting down of the production line is required and considerable time may be involved in the changing of the equipment.